Monumental Feats

When studying prehistoric times, massive burial monuments—Egypt’s pyramids, for example—often serve as signs of strong leaders rising to power. But among Pacific island regimes, deciphering exactly when transfers of power took place can be hampered by the degradation of building materials, or by imprecise research tools.

Recent technological advances have helped archaeologist Mark D. McCoy of Southern Methodist University and an international team of colleagues to pin down the earliest date yet for a burial monument in the Pacific, found on the Micronesian island of Pohnpei.

The complex architectural feat they examined is known as Nan Madol, former island capital and now a UNESCO World Heritage Site. Nan Madol’s impressive stone buildings sit on 98 artificial islets constructed on coral reef and separated by canals. Each islet is framed with double walls made of long basalt columns and filled with crushed coral. Oral tradition maintains that its biggest and most imposing structure was built to hold the remains of a chief who first unified the island community.

McCoy and his colleagues used laser scanners to create a 3D model of the monument’s architecture, focusing on its stone building blocks. They then used a portable X-ray fluorescence spectrometer to reveal the chemistry of particular stones, allowing researchers to trace the stones’ geological origins on the volcanic island. Finally, the team employed a uranium-thorium dating technique, which has greater precision than radio-carbon dating, to determine the age of the burial monument’s coral fill and therefore that of the main tomb.

The results push back the previous estimate of Nan Madol’s age—and therefore the solidification of political power on the island—by over a century. By the year 1180, the first ruler’s tomb was being erected out of huge basalt columns and boulders, sometimes weighing several tons, many of which were harvested from the farthest corner of Pohnpei. According to McCoy, “clearly this was important to the builders and if you didn’t know the geochemistry you’d have no idea.” By 1200, the central tomb held its occupant. This timeline makes Nan Madol the earliest evidence in Oceania of monument building, which eventually appeared on other remote Pacific islands in the following centuries. (Quaternary Research)